The invention relates to a method for controlling the operating voltage of a fan in electrical equipment.
For a power supply with fan cooling, a fan is frequently used whose rotation speed is controlled for noise reduction. Particularly in a quiet office environment, the fan noise using conventional temperature/rotation-speed control is nevertheless considered to be too loud in this case. When reducing the fan rotation speed, care must be taken to ensure that the electronic physical elements which are to be protected remain below the maximum permissible component temperature throughout the entire load and temperature range.
According to a previously known method, the air temperature of the power supply is converted into a control voltage for the fan with the aid of a power stage and a temperature-dependent physical element, for example using a so-called NTC or PTC thermistor, that is to say a resistor whose resistance becomes correspondingly greater when it is cooled down or heated up, respectively. The temperature/voltage characteristic which is used in this case is at the same time relatively flat or broad, that is to say the control voltage rises in a wide range, for example between 20.degree. Celsius and 60.degree. Celsius, from a basic voltage level to the maximum fan voltage.
In the case of some fan controllers, the temperature sensor is mounted on a heat sink of power components in the power supply so that the output power of the power supply is also taken into account when setting the fan operating voltage.
U.S. Pat. No. 5,197,858 discloses a temperature-controlled speed adjustment of fans in electrical equipment, which adjustment carries out the control of the fan in such a manner that the fan rotation speed is set to be constant at a first value up to a first equipment temperature limit. After this, the fan rotation speed is continuously increased up to a second equipment temperature limit. Above the second equipment temperature limit, the fan rotation speed remains constant.
In this context, a circuit arrangement is admittedly specified in which the respective equipment temperature limits can be adjusted between which the continuous rise in the fan rotation speed is intended to take place. However, only the principle is in fact specified as to how regulation of the fan rotation speed is intended to be carried out. The regulation of the fan rotation speed is admittedly related to a reduction in the fan noise. However, no proposal is made as to how the fan noise can be reduced to the maximum extent while maintaining the cooling function for an associated electrical equipment.
"PC-Lufterregler" (PC fan regulators) by Svenkerud/Kristiansen in DE-Z "Elektor" (Elector), Issue 7-8/92, page 22 discloses a circuit arrangement for controlling the fan RPM of a fan in an electrical apparatus, which, besides a start-up controlling, carries out a fan RPM controlling, such that after the fan is started up, the fan RPM is controlled continuously with an increasing temperature in the electrical apparatus. For this purpose, an inception point and an increase function for the controlling are defined. The inception point is at 2.degree. C. and the increasing is determined such that the fan RPM increases continually as the temperature increases up to a temperature of 30.degree. C. The basis for the controlling is the air temperature in the electrical apparatus, which the control range of 2.degree. C. through 30.degree. C. matches. With the proposed air controlling, a noise reduction is achieved, however, the noise reduction does not correspond to the noise reduction that could be maximally achieved